Rhenium, a scarce refractory metal, is not naturally occurring, but rather must be extracted as a byproduct of copper or molybdenum mining. Rhenium is not very reactive, reacting only slightly with nitric acid (HNO3) and not at all with hydrochloric acid (HCl) or sodium hydroxide (NaOH), for example. Rhenium is often found with molybdenum as part of a copper porphyry deposit. Commonly, rhenium is recovered from the flue gases emitted during roasting of molybdenite concentrates after subjecting the flue gases to quench liquors. Rhenium has also been known to have been recovered from uranium leach solutions.